In presence of NaCl the number of high affinity binding sites for 3H-cocaine increased by 2 to 3-fold. Lesions with 6-hydroxydopamine, but not kainic acid eliminated the Na+ dependent increase in binding. Drugs which can displace 3H-cocaine from its binding sites are strong inhibitors of 3H-dopamine uptake into rat striatal synaptosomes or slices. The present results suggest that Na+ dependent cocaine binding sites are located on presynaptic dopaminergic axons. In brain tissue there exist a pronase-sensitive and trypsin-resistent displacer for 3H-cocaine binding.